The SPECTRE d-GMM (Ground Movement Monitor) integrates a rugged magneto-strictive displacement sensor for geotechnical monitoring of rock deformation. It has an on-board microcontroller running YieldPoint’s proprietary d-Tech signal processing and transmission technology to provide a high precision single point displacement sensor.


The d-GMM is a single channel Ground Movement Monitor available with high resolution and data accuracy.

The microcontroller provides linearization, temperature compensation and outputs an ASCII encoded RS485 signal digital signal. Output signals can be transmitted over 250m/900ft without distortion. Each instrument is individually calibrated to ensure that the resolution (<0.01mm) and accuracy (0.25% typical) are an order of magnitude better than for similarly priced technology.

The digital form of the signals eliminates the necessity for expensive analog-to-digital conversion and results in low cost monitoring peripherals that output data in real world units (mm and degC). The instrumental is fully compatible with d-Logger, d-Mesh and d-Reader and can be networked using the IoT gateway.


Borehole size 30mm+
Core Technology Magnetostrictive displacement sensor
Output Signal RS485 serial (9600,8,N,1) ASCII-encoded digital signal
Stroke (F.S.) 145mm, 250mm
Displacement Resolution 0.01mm with handheld readout
Displacement Linearity Typically 0.25% F.S.
Displacement Accuracy Better than=/- 0.5mm
Temperature Range -40 to 125 degrees Celsius
Temperature Accuracy +/- 2oC –Digitally trimmed at 0oC and 25oC
Temperature Resolution Temperature Resolution: 0.1oC
Temperature coeff for eddy current sensor: <0.01%FS/oC (0-50oC)